With any high index contrast between waveguide and cladding, such as in silicon (Si) photonic systems or group III-V systems, any open port of a multi-port device, such as multi-mode interference (MMI) coupler, directional-coupler (DC), and Y-junction coupler, will cause strong back-reflection and/or scattering into the cladding. Back reflected or scattered light could get picked up by nearby components, adding to optical noise and cross-talk. In a standard design for a ridge waveguide defined in silicon (Si) and surrounded by a dielectric cladding, e.g. silicon-dioxide (SiO2), the refractive index of Si is ˜3.4 while the refractive index of SiO2 is ˜1.44. The high contrast between the Si and the SiO2 results in reflection of ˜20% (or −7 dB) of the light, if a waveguiding element is abruptly terminated, and the rest will be radiated into the substrate.
An object of the present invention is to overcome the shortcomings of the prior art by providing a dump terminator for controlling scattering of light and/or for absorption of light, while maintaining low reflection (<−30 dB).